My toys over the years

I showed the computer, the processing speed and the amount of memory in a table:

YearMachineCPU SpeedMegabytesProduct (Mhz*MB)

1971 PDP-8 .066.004 .000264

1981 IBM PC 4.77 .25 1.1925

1991 PC Clone 66 1 66

2005TabletPC 2000 2000 4,000,000

Both the processor speed and the RAM increased by several orders of magnitude over the decades. The Speed Memory product of my current tablet is 10 billion times (LOG10(4e6/.000264) => 1e10)greater than my first machine!

You have slightly underestimated the PDP-8. The memory on those things came in banks of 4k WORDS, not bytes. Since words were 12 bits, you actually had 6144 bytes of RAM, or .006 MB. Also, the cycle time of an original PDP-8 would be 1.5 microseconds, so it was more like 0.666 MHz.

This means the MB*MHz is actually .004. So you were off by a factor of 15, but it’s still 9 orders of magnitude difference! Of course a PDP-8 took 2 cycles to add 12-bit numbers, while today’s computers can do simultaneous adds of 32- and 64-bit numbers in a single cycle, so that extra order of magnitude should probably be figured in anyway.